Vaccination remains the single most valuable tool in the prevention of infectious disease. Nevertheless, there exists a need to improve the performance of existing vaccines such that fewer boosts are needed or to develop novel vaccines. For the development of effective vaccines for humans, a great need exists for safe and effective adjuvants. A number of novel adjuvants have been reported in recent years including: i) bacterial toxins such as cholera toxin, CT, and the Escherichia coli heat-labile enterotoxin, LT; ii) less toxic derivatives of CT and LT; iii) endogenous human immunomodulators, such as IL-2, IL-12, GM-CSF; iv) hormones; v) lipopeptides; vi) saponins, such as QS-21; vii) synthetic oligonucleotides containing CpG motifs (CpG ODN); viii) lipid 'A derivatives, such as monophosphoryl lipid A, MPL, and ix) muramyl dipeptide (MDP) derivatives. Herein, we will review recent findings using these novel adjuvant systems.